This application relates to a low pressure turbine for a gas turbine engine in which there are inner and outer counter-rotating blade sets, and wherein the two blade sets drive a common shaft to drive a fan.
Gas turbine engines are known and typically include a fan delivering air to compressor sections. The air is compressed and delivered into a combustor section where it is mixed with fuel and combusted. Products of this combustion pass downstream over turbine stages. Typically, there is a high pressure turbine over which the products of combustion expand to drive a shaft. The high pressure turbine typically drives a high pressure compressor in the compressor section. Downstream of the high pressure turbine is a low pressure turbine. The low pressure turbine has lower pressure products of combustion expand over its blades, to drive a low pressure compressor and a fan. Typically, the low pressure turbine may drive the fan at an undesirably high rate of speed. Thus, various steps are taken to lower the speed of the fan as driven by the low pressure turbine.
One common step is to include additional stages in the low pressure turbine. This is undesirable as it adds to the weight and complexity of the gas turbine engine.
It is also known to provide gearing between the shaft that is driven by the low pressure turbine and the fan to reduce the rate of speed of the fan.
It is also known to provide counter-rotating inner and outer rotor sets in the low pressure turbine. In this manner, the number of turbine stages is effectively increased by replacing the prior art static vanes with the rotating outer rotor stage. Typically, this has been utilized to drive components in the gas turbine engine through two separate shafts.